This article is a little bit of a tangent to my regular articles. I am presently doing an online course - Climate Change: Challenges and solutions - offered by the University of Exeter (UK). So please indulge me as I also use this blog for some climate course work. This article is for section 2.3 of the course on Snowball earth events that have ocurred in the distant past.
No one is sure what precipitated the onset of snowball earth events. The oldest snowball earth event occurred approximately 2200 million years ago. The most recent event ended about 635 million years ago and is thought to have lasted 6 to 12 million years. Very basic life managed to survive at least the most recent snowball earth event.
The earth's orbit around the sun, it's axial tilt, and wobble all have different millenial cycles which can affect the amount of solar radiation being absorbed by the earth. Earth’s orbit changes from near circular to oval shape on a 100,000-year cycle (eccentricity). Earth’s axis is tilted and is presently at 23.5 degrees. It varies between 21.5 and 24.5 degrees every 41,000 years (obliquity - Milankovitch cycles). As the Earth spins it wobbles on its axis toward and away from the Sun over the span of 19,000 to 23,000 years (precession).
What caused the earth to go into a giant snowball is still being debated in scientific circles. A number of theories have been advanced including :
- a reduction in solar output,
- the Earth passing through rare space clouds,
- a combination of high obliquity in the Earth's orbit, orbital eccentricity or precession;
- Lithospheric weathering reducing atmospheric carbon causing planetary cooling
